A risk assessment of mechanics who changed chrysotile asbestos containing brakes and other vehicle components in the 1950s-early 2000s era: an update on the 2004 evaluation.

Abstract

For the past 50 years, there has been an ongoing interest in understanding the potential health hazards, if any, to vehicle mechanics who worked with asbestos-containing brakes in the 1950s-early 2000s era. Two reviews have been published on this topic, one by Langer (2003) ("Reduction of the biological potential of chrysotile asbestos arising from conditions of service on brake pads") and another by Paustenbach, et al. (2004) ("Environmental and occupational health hazards associated with the presence of asbestos in brake linings and pads (1900 to present): a 'state-of-the-art' review"). This analysis is an update on those papers since a considerable amount of research has been published over the past 20 years on this topic. The following important aspects are addressed in this review: new information on the toxicology of chrysotile, toxicology studies of brake dust associated with grinding, additional epidemiology studies and meta-analyses published on auto mechanics of the era, previously unfound data on how brakes (during the era when chrysotile was used) were manufactured, and new work describing the transformation of chrysotile to various degradation products during vehicle braking. This update also addresses questions about the health hazards associated with asbestos in vehicle clutches, transmissions, and gaskets. The exposure data indicate that the airborne concentrations of chrysotile fibers associated with vehicle mechanic work when asbestos was in auto brakes were, on average, less than 0.04 f/cm³ (8-h TWA) and the average lifetime cumulative dose was in the vicinity of 0.5-3 f/cm³-year for mechanics of that era. Although many of these fibers may have no toxicity due to thermal degradation and the conversion to degradation products, 31 epidemiology studies have evaluated the risks of mesothelioma for vehicle mechanics of this era and all but one indicate that there was no increased incidence of this disease in these workers. The weight of evidence continues to indicate that the asbestos-related health risks to vehicle mechanics from asbestos-containing components were de minimis. The risks associated with take-home and bystander exposure of a mechanic were also addressed and they were found to pose a de minimis or zero health risk to those potentially exposed. Based on our evaluation, there is no indication that asbestos from asbestiform tremolite was present at detectable concentrations in bulk samples of brakes or in the air during brake work. The recent U.S. Environmental Protection Agency (EPA) risk assessment of 2024 on chrysotile and their views of the hazards of asbestos-containing brakes were discussed. Their analyses did not alter our views that exposures to mechanics posed no increased risk of asbestos related disease. The latest knowledge about the role of genetic susceptibility on the development of mesothelioma is also addressed.